That test was from 2020. I could not dig up the 2022 test. The high HCs are the same on each, but not sure about the CO, CO2 and O2. I am not sure what configuration the truck was in for the 2022 test that finally passed after 5 tries. The 2020 test took 7 tries. I did not keep records of what I did after each failed test, but whatever changes were in response to the various numbers.
On those roller tests, anyone know how much of a load is imposed at 1500 rpm and at 2500 rpm? How wide open is the throttle?
In this situation Iād take the truck to a dyno and test the HC going up and down a size on the main jets.
Might combustion chamber deposits be part of the cause? Have you tried a top end cleaning?
The black soot deposits likely occurred during choke operation, how many miles do you normally drive after the choke has opened?
Engines with a tailpipe output of 1% to 2% CO usually have clean spark plugs, your CO reading is near zero.
I was using the truck lately because I was changing a leaking radiator on my daily driver. I made a couple of 6 mile round trips over surface roads with enough time in between for the engine to cool down, and one 3 mile round trip, surface streets, again, with time for the engine to cool. Usually I donāt drive it unless I need a truck. The several times before this would have also been short trips. I need to take it out on the freeway and burn a gallon or two, and then check a plug again.
The last test I took in 2022 (found it) the rpms for the dyno test were 1214rpm at 15mph, and 1234rpm at 25mph. I donāt know if that is helpful in determining the load, but it is greater than driving on a level street at those rpms. A slight upgrade would impose a load that would yield those speeds at those rpms. I couldnāt place a number on the grade.
Looking at the emissions test results posted previously, the carb was already jetted too lean (in my opinion) and lowering the CO level will certainly cause the NOx and HC to rise, which is the opposite of what he wants.
Having spent years and years using a gas analyzer and emissions tests, if I were working on this truck a Motorvac service would be the first thing I would do.
7 emissions tests? How did this not end up at a referee?
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I bet youāre right, thatās why I recommended trying smaller and bigger jets instead of just putting in smaller jets. It might show bigger ones would be better.
If @Fresno-Jack jack had access to a tailpipe emissions HC analyzer he could try the various ideas and report back which ideas work the best at reducing HC. I wonder if such a thing exists thatās affordable (or rentable) for a diyāer? If so, thatād be the way to go. There are inexpensive silicon hydrocarbon sensors available to the diyāer electronics hobbyist. Googling should find quite a few. These gadgets arenāt usually calibrated in PPM, but are specād for a certain range of ppm, & would tell you if the HCās went up vs down after making a change.
It seems you are on the right track there OP, best of luck. Maybe someday your classic truck will be exempt from tailpipe testing.
Buy a 5-gas analyzer, rent a dynamometer, open the carburetor 6 times to change the jets, is this what people do for fun?
If I had to open the carburetor, I would just clean the existing jets with a jewelers file, maybe enough to enlarge the jets by 0.005".
Thereās probably a good deal of money to be made for someone who invents and markets an inexpensive diyāer friendly HC exhaust gas analyzer. Generally diyāers donāt need all 5 gasses, just the HC.
Heās done it before, and heās taken 7 times to pass, so it seems like spending the money to dyno it would save time, overall.
Trying to correct high HC without seeing CO, O2, and CO2 would be like throwing darts blindfolded. You need all 4 to do the math.
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Iām guessing op never made an appointment with the referee
There are portable gas analyzers available, but theyāre generally quite expensive
And you need to know all the gases to get the ābig pictureā
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Cleaning the carbon from the top end. Three quarts run through. One quart to go. Punched a small hole in the cap, cut off the bottom. Top off as needed.
Are those 5 hose clamps on your AC suction hose all spares?? lol
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What values would you want to see, compared to these?
Does the O2 at around 4% mean heās already lean?
Sharp eye! I suspected a leak about decade or two ago. Got a larger hose, split it, smeared it with some kind smelly glue or caulk and clamped it on. As it turned out the the leak caused by metal gaskets. I replaced them with AC o-rings and havenāt had a leak since. I replaced all the AC components. When the compressor finally conked out about a year ago.
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The O2 always tests zero or maybe 0.1 % on the Corolla. Iāve never seen anything more than that . But maybe thatās just b/c the Corolla is fuel injected, OPās truck is carbād. Apples to oranges.
No dispute. But Calif emissions testing provides the car owner all of that info already. Iām referring to pre-test experimentation when the car owner knows from prior year testing that excess HC is the most likely reason for not passing. In that situation a diyāer having access to the HC tailpipe levels, even if not calibrated to PPM, would still be pretty helpful. Try this, does HC go up or down? etc. Diyāers wouldnāt own the roller treadmill that the testing shop has though, so would have to do all the tests at various rpms in the driveway.
Thanks, I took this advice to heart and went back to the trusty emissions chart.
Based on the test results I posted earlier, it definitely looks like I am well to the right of 14.7. A minor tweak to a richer mix should help. I replaced the ~1.32mm jets with a pair measuring ~1.40mm. The Holley 2280/6280 carburetors used main jets manufactured for Weber DCD/IDA/DGV/DGAV/ICT Carburetors.
After installing all the new ignition parts I checked the timing. It was still at 9Āŗ BTDC where I had set it for the last smog check two year ago. I dropped it to 5Āŗ BTDC. 7Āŗ BTDC is factory spec. This, coupled with a slightly richer mix and a much more powerful coil, should help. I have until the end of May to take the test, so no hurry. All the work I had in mind has been done, but I am certainly open to any further suggestions.
Jack
Well in this case we have to account for an Air Injection System that is artificially increasing the O2 amount in the exhaust stream. Without the smog pump, Iād hope for about 1% O2. But given the very low CO and the marginal HC readings I would say itās lean to the point of raising HC. Coupled with the NOx readings that tell me itās a little too hot in the combustion chamber, I would want to richen the mixture to cool down the flame and reduce both HC and NOx. Thereās plenty of room to increase CO. But I still think, given the age of the truck, much of this is caused by excess carbon deposits.
Thereās no point in getting the HC down if doing so raises another emission gas past the limit. If you donāt see the whole picture youāre no further ahead.
Doesnāt your truck have a smog pump or secondary air injection system? If so these figures will have to be adjusted to compensate for the added O2 in the exhaust.